Additive for a well servicing composition



July 3, 1962 G. R. MORRIS Filed April 17, 196i DUST DRYER STORAGE HOPPER 4 Sheets-Sheet 1' CHUNKS LAMINATES SORTING CRUSHING BREAKING HAMMER MILL II HAMMER MILL It 2 STORAGE HOPPER SCREENS f1 .2 I J BAGGING APPARATUS "5 ")5 r/ I i I l f I I 1 ENTOR I05 IIO I05 George R. Morris ATTORNEYS July 3, 1962 G. R. MORRIS ADDITIVE FOR A WELL SERVICING COMPOSITION Filed April 17, 1961 4 Sheets-Sheet 2 Super Course Grade Cone Fiber OPENING SEALED (INCHES) INVENTOR George R.Morris BY fia W ATTORNEYS July 3, 19,62 G. R. MORRIS ADDITIVE FOR A WELL SERVICING COMPOSITION Filed April 17, 1961 4 Sheets-Sheet 4 mm OOI mm s:

um: 92 V mm 02 I u w w mm a =ou2aa 2.5234 22:00 :o 033 2:50 E2530 INVENTQR George R. Moms United States Filed Apr. 17, 1961, Ser. No. 103,361 13 Claims. (Cl. 252-8.5)'

This invention relates to fluid additive compositions for preventing or reducing the flow of fluid through permeable structures. More particularly the invention relates to ad ditives for fluid such as drilling muds, cement slurries, and

. the like to prevent or retard lost circulation, seepage, and

filtration losses. This application is a continuation-in-part of my copending application Serial No. 24,423 filed April 25, 1960, now abandoned and which in turn is a continuation-in-part of my copending application Serial No. 677,210 filed August 9, 1957, now abandoned and Serial No. 15,837 (a continuation-in-part of Serial No. 677,210) filed March 18, 1960, now abandoned.

The loss of either the fluid phase of drilling ,mud' by filtration, or the loss of both solid and liquid phases of the mud known as lost circulation, and the loss of cement slurries through permeable rock structures, has long been a serious problem. Except in special instances, the standard methods used to control-the aforementioned are by mechanical sealing agents to check circulation loss and by the use of organic materials to stop or minimize filtration losses or in the case of cement, by combining the effects of decreasing its density and adding mechanical sealing agents.

Drilling fluids are very important in modern drilling methods since they perform several important functions. For example, the, fluid reduces the frictional resistance encountered by the bit in drilling a formation and by the drill pipe in rotating against the side of the hole; it provides for the proper removal of cuttings from the hole; it cools the bit and thereforereduces galling; it has a wall-building property which .causes a thin cake of solid suspended particles to form around the borehole which is more or less fluid-impervious and prevents fluid in the well from penetrating into and being wasted in the surrounding earth formations. It, also, prevents the cuttings that are suspended and being removed from the borehole from settling to the bottom of the hole during suspended drilling operations due to a thixotropic characteristic and, in addition, has'several other functions as is Well known.

A drilling fluid can be obtained by modern methods which Will perform all of these functions very eflectively but there are certain conditions which must be maintained in the fluid to provide this effectiveness. For example, the mud viscosity and gel strength must be maintained at certain degrees to provide the thixotropic property for adequate settling of the cuttings to take place in the surface pits without troublesome settling in the boreholes. Also, the pH value of the mud should be controlled to insure for a particular mud, that its other properties will remain stabilized. Therefore, it is desirable when treating the drilling fluid with a lost circulation and/ or filtration loss additive that the various properties such as viscosity, alkalinity, weight, gel strength, etc. remain unchanged, otherwise, in addition to adding the filtration loss additive, other additives will be required to restore the drilling fluid to its desired original state.

Undesirable losses of the drilling mud to porous thief "formations having cracks or fissures, the openings of It is usually l 7 3,042,608 Patented July 3, 1962 eliminating the loss of the mud. The normal procedure is to try the addition of sealing or plugging agents to the drilling mud for sealing or bridging the pores or fissures of the sub-surface formation. If the plugging agents are not successful in reducing the fluid loss, it is the usual procedure to use chemical agents or cement in an effort to control the lost circulation. The Well drilling technique may also be controlled in various ways such as by altering the mud weight or the circulation pump pressure or by changing the physical properties of the mud (viscosity or gel strength, for example).

In addition to lost circulation, filtration and/ or seepage losses are commonly encountered drilling problems. Seepage is a problem primarily incurred while 'spuddingin although it may continue during the entire drilling phase as well.

Seepage losses of mud are not considered to be lost circulation. Such losses can amount to several barrels per hour and are common to the type drilling in the interior United States, where water or very low-solid muds are used.

Frequently, formations near the surface are loose soils, sand and gravel, and the spud mud is designed to Wall these formations, to prevent caving and hole enlargements, and to have suflicient body to carry out the cuttings and gravel in this fast drilling section. Usually, if the mud is capable of Walling the formations, seepage occurs and water is added to the mud pit in proportion to the quantity of water lost to the borehole formation and lost in the mud pit. In areas where Water costs are excessively high it is obvious that there is an urgent demand for the reduction of seepage losses. In the following description the statements in regard to filtration losses are equally applicable'to seepage losses since both primarily involve a loss of water (or low-solid fluids).

It is desirable to reduce the filtration loss from drilling fluids for several reasons, one of which is the fact that an excessive fluid loss means that large quantities of fluid flow through the borehole wall mud sheath and into the permeable formations leaving a Wall cake behind which may become so thick as to seriously interfere with the movement of the drill pipe when it is withdrawn and may even result in sticking the pipe. Also, if a thick cake is formed over the face of the producing formation, it may not become properly cleaned off during the well completion process and Will interfere with the production rate of the Well. Further, the fluid which passes into the for- 'mation may also exercise a harmful effect on the drilling fluid to formations comprised of shales or clays of the types susceptible to hydration; the high fluid loss may result in swelling and heaving of the shale, slow drilling rates, fishing jobs and perhaps even ultimate loss of the hole. "If the producing formations contain hydratable clays, the intrusion of water may result in swelling of the clay particles within the sandy formation and permanent loss of permeability with resulting impaired production rates. Also, loss of fluid to the adjacent formations necessarily alters characteristics such as viscosity of the drilling fluid. An increase of viscosity requires much more pump power and slower drilling rates, and therefore higher costs in drilling to circulate the more viscous mud.

cementing operations also pose manyproblems in the oil industry. The changes which take place after ground cement has been mixed with water are somewhat uncertain and complex. Most authorities agree, however, that the setting of cement occurs in three periods: the socalled initial set, the final set and the hardening period. The initial set issaid to have occurred when the or most effective control method to apply for reducing or slurry has lost its plasticity. After the initial set has occurred, the cement undergoes further changes as a result of which it acquires hardness until the .final set is reached. Following the final set, a 7- to 28- day period of further changes takes place which results in a gradual increase in strength and hardness.

The time elapsed between the addition of water to ground cement and the initial set, plus the compressive strength and hardness are important as a result of the growing trend toward deep well completions. As the depth of completion increases the compressive strength, hardness, and setting time of the cement must increase due to elevated temperatures and pressures which may be encountered.

While many natural or hydraulically made lost circulation zones may be encountered before completion of a well, the number may be reduced or their effects minimized. At the time of cementing, many weak formations which cause lost circulation are fractured due to the difference in pressure between the formation and the high density column of fluid. Generally, the two common methods of reducing lost circulation while cementing involve either the addition of bridging agents or reducing the cement density. Both methods can be followed and improved results can be obtained in accord with my invention and discoveries as will be described hereinafter in detail.

Briefly, the present invention contemplates the use of resinoid particles in various forms or embodiments, with or without the addition of other materials, as a fluid additive to seal openings. The particular embodiment of my additive will, in general, depend on the service for which it is being utilized, i.e., for example as a lost circulation additive for well servicing fluids such as drilling muds and cement slurries, as a filtration loss drilling fluid additive, as a drilling fluid additive wherein the above mentioned lost circulation and filtration loss additives are combined, or as a seepage loss additive.

The addition of particulate materials to drilling muds and cement slurries is old per se. Some prior additives are hard nut shells such as walnut and pecan shells, peach pits, coconut shells, hard rubber, hay, excelsior, chicken feathers, cork, and leather. The use of plastic materials in a thermoplastic state is also known. For example, US. Patent 2,943,697 to Scott discloses the use of polystyrene. Similarly, U.S. Patent 2,912,380 to Groves and US. Patent 2,815,079 to Goins each discloses thermoplastic materials for use in well servicing operations. These materials are, for example, the hydrophobic vinyl resins, and thermosetting plastics in their thermoplastic condition such as phenol-formaldehyde, melamine-formaldehyde, and others. The use of phenol-formaldehyde in a thermoplastic state is also disclosed in Salathiel Patent No. 2,861,312 wherein a sulfonated, water soluble phenolformaldehyde is placed in a drilling fluid.

The present invention is distinguished from these and other prior art disclosures in that my materials are thermoset (C-stage) resinoids which are hard, infusible, insoluble, and are easily adapted to provide improved additives for well servicing fluids such as cement slurries and drilling mud.

Accordingly, the primary object of this invention is to provide a compositionof matter composed primarily of thermoset materials for use in well servicing fluids such as a cement slurry or drilling mud and which is capable of bridging or otherwise closing formation openings when carried into contact with the openings by such fluids.

Other objects of this invention are to provide:

(1) An additive for well servicing fluids which will not materially alter the physical properties of the fluid, but which will prevent lost circulation during the drilling, cementing operations, or the like; (2) An additive of thermoset material in various forms for drilling mud which will not materially alter the physical properties of the mud but which will prevent or control lost circulation and/or filtration losses in either fresh water, salt water, or lime base drilling muds;

(3) An additive for well drilling fluids which increases the strength and impermeable character of the mud sheath on the well bore wall, and which is capable of withstanding high pressure and temperature for increasing the efficiency of the bridging of openings such as fissure or fractures in sub-surface formations;

(4) An improved drilling fluid additive having a substantial amount of relatively flat and strong particles capable of bridging formation openings and withstanding high temperatures and pressures;

(5) A novel drilling fluid additive comprising thermoset particles, a substantial amount of which are relatively flat, have a high flexural strength, and will not give misleading or deceptive fluorescence;

(6) A borehole mud sheath composed of mud and thermoset particles which substantially prevents or terminates lost circulation; some of the particles bridging openings in the borehole while others are collected over and around the bridging particles, whereby a substantially impervious, yet strong and unobstructive barrier is formed to contain the borehole fluids;

(7) A novel process for making a drilling fluid additive comprising producing particles of thermoset material in specially adapted crushing, breaking, and sizing apparatus, and bagging for use;

(8) A colloidal drilling fluid additive of thermoset material and an organic material primarily for preventing filtration losses during a drilling operation;

(9) An additive for drilling mud which can be adapted to pass readily and easily through the pumping equipment and causes little or no wear on the working parts thereof; and,

(10) Novel cement slurry additives to prevent lost circulation of the cement, and to reduce the density of the slurry without the normal attendant loss of compressive strength.

Other objects and advantages of the invention will become apparent to those skilled in this art from the appended claims, and the following description with reference to the accompanying drawings wherein:

FIGURE 1 is a schematic flow sheet illustrating the novel processing steps to which thermoset materials are exposed in making additives of my invention;

FIGURE 2 is a schematic diagram of an attrition mill employed in my novel process of manufacturing additive in accord with myinvention;

FIGURE 2a is a chart showing test results for determining the slot sizes which my additives'can seal at various concentrations as compared with prior art additives;

FIGURE 3 is a chart showing test results of thermoset additives in accord with this invention employed as a drilling fluid additive as compared to results obtained under the same conditions for other prior art additives; and,

FIGURE 4 is a graph which illustrates the ideal size gradation curve for the particles employed in my lost circulation additive; the illustration being made with particles ranging in size from 4 to 200 Tyler mesh.

MATERIALS I have discovered that thermosetting materials provide particularly good results when used as additives in accordance with my invention. These materials initially form in a liquid A-stage from which B and C-stage plastics are made. Stage B is formed from stage A by the use of heat and an accelerator acid catalyst, and is then commonly converted to its insoluble, infusible C-stage as it is used for manufacturing finished molded products. Plastics utilized in my invention are in their C-stage state as opposed to heat softenable thermoplastic materials or A- or B-stage materials which are relatively soft and weak in comparison to C-stage materials.

In general, two types of polymers characterize two entirely different classes of plastics, i.e., thermoplastic and thermosetting materials. The linear or chain polymers are thermoplastic. Thermosetting resinoids on the other hand are formed once a three-dimensional cross-linked molecular structure is established.

The production of thermosetting materials is well encountered in deeper wells.

known. Phenol-formaldehyde for example is commercially available from American Cyanamid and Formica Corporation. It may be produced from phenol in condensation with formaldehyde which can be effected with either an alkaline or an acid catalyst. The initial reaction is the addition of phenol at one of its active ortho or para positions to the carbonyl band of formaldehyde. Repetition of this leads to a progressively more complicated network of cross-linked chains made possible by the three active positions on the phenol nucleus. Such crosslinked, three dimensional structures are not fusible. In practice the reaction is controlled for example, by the time, temperature, choice of catalyst, etc. to produce the A, B and C stages.

, Any C-stage thermoset material may be utilized in accord with my invention; however, particularly good results have been obtained from phenol-formaldehyde, melamine-formaldehyde, epoxy and urea-formaldehyde materials. 'I prefer to use C-stage phenol-formaldehyde in my additives primarily because it is economical and exhibits particularly good physical characteristics of the type desired in a drilling fluid additive.

Other suitable materials may be found, for example, in the Plastics Properties ChartEncyclopedia Issue- 1961, part II Thermosets published by Plastics Catalogue Corp. The materials cited on the chart are normally used in industry as molding or casting compounds; examples of those listed follow, each accompanied by at least one tradename under which it is currently marketed:

Diallyl phthalate Dapon, Diallr Polyacrylic ester Hycar PA. Polyester resin Lamin-ac, Glykon. Al-lyl resins Cocor,Erduron. Glyceryl phthalate Poly-phen. Casein plastics Galom, Ameroid.

Industrial phenol-formaldehyde is commonly used for many purposes in industry, usually with a filler material such as wood flour, cotton linters, etc. which impart additional strength. Many lamination manufacturers use this material extensively in its A-stage state, by impregnating layers of paper, clot-h, asbestos paper, glass and glass fabric, wood, etc. The impregnated layers are laid one upon another to build up the desired thickness and are bonded into a unit by heating under pressure, the plastic being cured to its C-stage. Plastic products thus produced are usually machined into a variety of useable articles, or cast sheets thereof are cut into desired usable sizes. As a re sult of this sizing and machining there is normally a considerable wastage of the industrial plastic material, and since there is no known practical way today for reversing the plastic forming process from C-stage back to A' or B- stage, the waste product is usually discarded primarily due to the fact that it is infusible. These scraps or waste products may be utilized in the preparation of my well servicing fluid additives, thereby providing an inexpensive raw material, as well as providing an efiicient usage for products which are normally discarded as of no value. The following is a list of advantageous properties exhibited by my improved additives.

(1) They provide all the advantages of prior art additives. t

(2) They are not only insoluble in Water and oil, but also in acids and alkalies, and in general in chemical solutions of the type capable of dissolving other types of plastics such as nylon, polystyrene, and lucite for example.

(3) Thermosetting materials are infusible th'us permitting their use in deep Well drilling and servicing under temperatures in the order of 550 :F. Thermoplastics have the disadvantage of melting under high temperatures The molten plastic tends to coat the drill bit, shale shaker, and all other parts of the drilling apparatus with which it comes in contact.

4) Thermosetting materials are very strong, having a compressive strength in the order of about 30,000 p.s.i

into the mud pit coarse and return to the mud pit in very fine sizes.

{5) The ther-mosetting materials are easily mixed with all types of muds and will not settle out.

(6) Friction is reduced in the drilling system and there is no appreciable resultant abrasion or coating of the drilling equipment due to the nature of the thermosetting material. This has obvious advantages over materials suggested by the prior art which are softer A and B stage materials which stick or coat equipmentand over hard predominantly granular shaped material which cause wear on the equipment.

(7) Drilling mud properties are not materially altered; this is particularly true of viscosity and pH.

(8) Thermoset materials do not produce misleading fluorescence, or give false electric log readings. All materials will fluoresce if subjected to certain irradiation treatments. The characteristic fluoresence of thermoset materials is an almost undetectable faint rose color. The difierence between this very faint fluorescence, and the fluorescence of crude oil and paraffins is readily apparent and detectable to servicing groups such as core analysts.

In the above cited Groves, Goins and Scott patents however, the disclosed thermoplastic materials are characterized by a peculiar fluorescence that would indicate the presence of hydrocarbons and petroleum to the extent that even the most experienced service personnel are sometimes misled.

Thermoset materials may be used in my additives individually i.e. (in substantially pure quantities) or in combination with each other and with materials with which they are used in industry as mentioned above. Materials such as wood flour, walnut shell flour, chopped fabric, cotton flock, chopped canvas, asbestos, etc. in general increase the strength of the C-stage resiuoid and do not react in conventional drilling muds or cement slurries. Accordingly, it will be understood that industrial plastics as used in the present specification and claims refers to those commercial materials such as the described laminates which, when crushed, will produce particles of pure thermoset plastic as well as particles including the filler materials. An organic constituent such as carboxymethylcellulose or hydroxyethylcellulose may also be added to my composition, particularly when the thermoset material is used in dust form, to prevent filtration loss.

Thermoset materials having a refractory or heat resistant material included therein such as glass base thermoset materials are particularly useful in drilling operations encountering very high temperatures. Such materialsare for example, polyester and alkyd resinoids reinforced with fiber glass such as currently marketed under the tradenames Glastic, Durez, Atlac, and Blaskyd. Other examples are epoxy resinoids made more stable by the inclusion of a silica filler and currently marketed under the tradenames Epi-Rez, Hysol, and Stycast. Again, any thermoset materials will be suitable for my purposes since it is the thermoset characteristic which produces the novel results of the present invention.

A satisfactory seepage preventionadditive can have less particle strength than is required of the lost circu lation additive particles. It is therefore possible to utilize the waste products from my process for making the stronger lost circulation additives, in making seepage additives. 'Such materials comprise thin laminated particles of filler material impregnated or coated with a resinoid, but which are relatively thin and pliable as compared to my lost circulation additive particles. A

I particularly suitable carrier material is'kraft paper coated or impregnated with C-stage phenol-formaldehyde or melamine-formaldehyde.

The particles are laminated as opposed to lamellar thermoplastic materials such as cellophane and celluloid. In general, best results are obtained when the seepage additive is composed of a majority of thin plate-like particles with the balance made up of flock-like material. However, it will be understood that the relative amounts of these materials may vary considerably. Thus, for example, the flock-like material is not essential and may be eliminated.

SIZE

The optimum size of the additive particles will vary according to the character of the formations encountered by the additive, and the purpose for which the additive is being used i.e., lost circulation, filtration loss and seepage loss for example. The variable factors that go together to make up the character of a formation being drilled are virtually innumerable. Generally speaking the bigger or larger the porosity, crack, induced fracture or other such condition contributing to lost circulation, the larger the particles should be. Accordingly, while any particle size distribution will be effective to block the passages through which fluid may escape in a formation, particularly good results can be obtained by trial and error treatments or if accurate formation data exists, by selecting a grade of particles in which a substantial proportion thereof would be capable of bridging the largest opening in the formation.

Ordinarily, the criteria for selecting the proper size of lost circulation materials and for determining when the additive is needed, may come from surface observations well known in this art such as for example, when the whole mud in the mud pit begins to decrease. When the loss of quantities of whole mud to the formation is apparent and the loss is evidenced by complete or partial loss of returns, the pumps are shut down. The hole may stand full or the fluid level may drop to where it balances the hydrostatic pressure of the fluids in the exposed formations, or when the entire mud pit may be emptied in a matter of seconds. The latter evidences (l) cavernous, open fissured or vugular formations and a coarse grade of lost circulation will provide better results that a finely graded material. Other formations that provide less apparent indicia are the coarser permeable formations such as gravels, reefs or vuggy limestone, or faulted joined and fissured formations or zones and it is recommended that a finer grind be tried first when such formations are indicated. Following the above size selection parameter, a person skilled in this art may readily select an initial size or grade of lost circulation, and subsequently select other grades until lost circulation is terminated.

Three basic types of thief zones which normally occur are highly porous and coarsely permeable unconsolidated formations, vugular and cavernous, and faulted, jointed and fissured. The last type includes natural or existing fissures as well as man-made or induced fractures. The conditions which enable a formation to take mud may differ very radically from one location to the next and in fact quite often differ in character in the same field or location. In many cases natural fractures exist, but are not permeable under normal conditions. However, when a critical pressure is reached in the hole, they open, take mud, and widen by wash out and take more mud.

This is encouraged to a certain extent by completely.

granular additives such as disclosed in the cited Scott patent. Even though pressure is later reduced, the opening may not close completely, and loss of circulation continues.

The latter is only one reason why it is much better in some cases, where formation fractures may be easily induced by high density and high hydrostatic head pressure, to pretreat by including an additive having a substantial percentage of flat two dimensional particles in the mud as a prophylactic measure to prevent lost circulation rather than to permit it to occur before treating. When used in pretreating it is almost impossible to determine what size material will best prevent fracturing, however, the same general rule regarding the relation of the largest size opening and particles capable of bridging the same is preferred.

As will be discussed below, the lost circulation additives of the present invention are produced by crushing industrial laminate and decorative thermoset sheet stock which may or may not include small amounts of conventional additive materials, which are hereinafter referred to simply as commercial thermoset plastic or resinoid materials for convenience, and which may be for economical purposes, waste materials from known processes, if desired. By the very nature of a crushing operation, control of resultant particle size is difiicult, but can be achieved by manipulation of the crushing apparatus to a certain extent. Therefore, while I prefer to use a graduated particle size distribution in my additives to obtain a thoroughly filled-in, strong, and relatively impervious barrier, I have found that it is not practical or essential to calculate and painstakingly distribute various particle sizes in specific amounts throughout the additive.

On the other hand, a gradated additive provides optimum results, and I have found it convenient and practical to classify my thermoset additives into five particle size gradation classes which may be selected for use as desired utilizing the foregoing size criteria. The five classifications are illustrative of the size distribution which I prefer and should not be construed as defining the limits of operability of my invention in any manner. For example, additives containing relatively large particles in the order of 1 /2 to 2 inches have been custom made and found effective in certain jobs although a maximum size of about one inch is generally preferable. For a particular purpose it may be desirable to utilize particles of all sizes in a single additive or to combine the below listed grades in any manner.

The preferred size ranges are:

Grade:

Fine Particles ranging from 150 U.S.

sieve size to inch.

Coarse fine Particles ranging from 150 U.S.

sieve size to inch.

Medium Particles ranging from U.S.

sieve size to inch.

Coarse Particles ranging from 100 U.S.

sieve size to /2 inch.

Super coarse Particles ranging from 100 U.S.

sieve size to 1 (one) inch.

The particles size distribution in each size grade will ideally be distributed throughout the range substantially as shown in FIGURE 4 for an additive having particle sizes ranging from 4 to 200 Tyler mesh. The ideal cement aggregate approach applies to the preferred grades given and disclosed herein, although I now generally prefer'larger particles than those given in the graph.

As will be appreciated by those skilled in this art, the cited particle ranges illustrate ranges of particle sizes now commercially preferred since they vary sufliciently to afford a suitable material for most conditions now encountered in Well drilling operations. The relative amounts of particles of certain sizes falling within the cited ranges are not critical although I have found that the larger sized particles within the ranges are preferably more abundant. Thus, in any one of the above cited ranges approximately 50% by weight of the particles are in the upper /3 of the size gradation, as shown in FIGURE 4.

Seepage losses can be prevented by the fine and coarse fine lost circulation materials above described, or by the impregnated carrier materials which constitute unuseable 9 by-products when the commercial resinoid material is crushed to make lost circulation additives.

These materials are unuseable under high pressures and temperatures since they are composed of a relatively large amount of filler material, predominantly kraft paper. The size of the latter is preferably maintained in the order of inch or smaller. A suitable seepage loss additive therefore may consist of kraft paper impregnated with C-stage urea-formaldehyde or phenol-formaldehyde. The particles, although very thin, are surprisingly tough and somewhat flexible, and not brittle as might be assumed.

To prevent filtration losses, particles size ranging from 150 Tyler mesh or smaller are preferred. The materials used for this purpose are discussed in detail below.

SHAPE Although my additives will obtain good results irrespective of shape, I have discovered that superior results are obtained when additives composed predominantly of relatively flat chip-like particles are utilized. By chipshape is meant particles which are relatively flat without regard to whether they are oblong or equidimensional as viewed towards the flat side. The thickness of the particles cannot be controlled in production and accordingly there is no correlation between the diameter and thickness of the particles. All that is necessary insofar as thickness is concerned is that the individual particles be sufficiently thick to possess a substantial portion of the -flexural strength characteristic of the thermoset material of which it is made. Flexural strength is the single most important characteristic of the thermoset materials inasmuch as it is this property which enables them to with stand high pressures when bridgingly positioned over an opening in a formation. Tests conducted on with particles of /2 inch diameter showed that the thickness usually varies from about .02 inch to .08 inch. It will be appreciated, however, from the unusual method employed in making the lost circulation additive, control of particles thickness is difficult, but since relatively thin materials may be used and are in fact preferred, thickness and flexural strength become critical only when the particles produced are paper thin. Such materials are excluded and saved for application in a seepage loss additive. Sliver and flock-like portions may also be used with the chiplike particles since they will fill in the spaces between and cover the chip-like particles to form a strong, impervious borehole lining.

Because thermoset materials are chemically and thermally inert and have a high tensile, flexural and compressive strength, they are capable of retaining their sealing ability under practically any conditions and after prolonged use.

Due to the relatively high hydrostatic pressures involved in drilling wells, a condition similar to that developed in fracturing a well may occur when granular particles are used to a large extent as a loss circulation additive, i.e., increased pressures in the borehole may tend to push these particles into the formation and create or enlarge fractures. Granular particles have been commonly used in fracturing materials as propping agents to improve porosity or open formations. Granules such tively large cracks or openings in the formation and due to their high strength remain in a bridging position. If the additive particles were flexible or weak in compression, normal operating pressures would have a tendency to bend or break the particles and force them into the formation thereby preventing the particles from performing their intended function. V

The primary purpose of any mud additive is to produce an impervious lining on the bore hole of the well being drilled to prevent loss of drilling fluid to the formations. This lining should be strong, thin, and of such a nature as to prevent fracturing of the formation it is attempting to seal. The resultant forces created by the fluid pressures in the bore hole acting on fiat particles after they have been positioned against the bore hole wall act in a direction perpendicular to the bore hole wall surface. Due to the fiat particle characteristics, this force is transmitted to the formation wall in the same direction, thatv is, perpendicular to the bore hole with the resulting net effect that forces applied through the particles to the formation are directed outwardly from the Well bore and not in an eccentric direction such as would cause fracturing or sloughing. Thus, it will be apparent that not only do my improved additives have advantages due to the nature of the material utilized, but also due to other factors such as the shape and size of particles which I use.

The preferred chip-like shape of my particles is one which has substantial length and/ or width, but has much less depth or thickness. Lamellated or thin scale-like particles such as mica and cellophane particles are unsuitable for my purposes in that they are not strong enough to withstand pressures encountered in bridging formation openings.

For use in controlling lost circulation I prefer to use a mixture of thermoset plastic materials having 3 to 100% by weight of chip-like particles with the balance sliver and flocklike particles preferably below 100 mesh size. Optimum results are obtained when the percentage of chip shape particles is between 65-98% with the remainder being substantially aqual amounts of flock and sliver like materials. When the problem is one of filtration losses alone a permeability in the order of only 325 as nut shells for'example, normally appear in most instances as three-dimensional wedge shaped objects. As :each such granule is carried by the drilling fluid it orients itself perpendicular to the flowing lines of the fluid. As these particles enter openings in porous formations, it has been shown by test that theytransmit forces created by the hydrostatic pressure with substantial components l in directions tending to widen the openings or cracks millidarcies is common and openings to be sealed are therefore very small. In suchcases dust-like material in the order of Tyler mesh (in largest dimension) is recommended. It is diflicult to control the shape of the particles at this size level although, sincethey are produced from laminated plastics a large percentage of the particles will be chip-shape.

Where the problem is one of seepage relatively high pressures are not present and the formations are usually relatively soft. For these reasons lighter, lamellar particles can be used to prevent Water losses through the borehole wall.

It is impossible from a practical standpoint to specify the exactpercentages of each size and shape of the particles that would provide satisfactory results. In some wells as little as three percent chip-like particles will impart the desired effect whereas in other Wells a much higher percentage by weight will be required to produce satisfactory results. By rule of thumb it can be said that the'coarser or larger grades have greater amounts of chips than the smaller or finer grades. This is primarily attributable to the method of producing the additive which involves crushing and grinding, since the smaller the grind the more difiicult it is to control shape of particles. It is recommended, for optimum results, that as high a percentage'ofchip laminates as possible be utilized in all grades. I

CONCENTRATIONS The recommended concentration of lost circulation, filtrat1on loss,'or seepage loss materials in the drilling fluid depends in part on the particular typeof Well op:-

acaaeos eration in which the fluid is used and in part on the geology of the formations at the particular location. As little as %;4/2 lb. per bbl. has been found to reduce lost circulation, however, under usual drilling conditions at least 3-5 lbs. per bbl. should be used. A practical upper concentration limit Would be about 4-0 lbs. per bbl., although it is possible from a technical standpoint to use concentrations up to the point where the drilling fluid can no longer be pumped. The latter would probably never be used in practice due to reasons of economies and drilling practices which require a workable drilling fluid.

Seepage loss materials may be used in amounts ranging from %50 lbs. per bbl. with good results obtainable throughout the range depending upon the conditions involved.

Powdered filtration loss materials are most effective in amounts ranging from llbs. per bbl.

METHOD OF PRODUCTION Laminated and decorative thermoset sheet stock materials are the most suitable materials from which thin chip-like particles can be made that will have the flexural strength to stand up under the extreme pressures encountered in deep wells.

Since residual resinoid materials may be obtained from various types of manufacturers, a diflicult problem arose as to how this material could be processed into a consistent form to be used in a drilling fluid. I have developed a process for making the drilling fluid additive of this invention which overcomes the problems such as those posed by the hard, infusible, insoluble character of the resinoids and the fact that some may be obtained in very large chunks, layers, or in dust form, and in some cases with a high degree of impurities. The latter is the subject of considerable importance since some manufacturers add metal such as copper to the resinoid which would have an adverse effect on well logging processes and possibly on subsequent well treating processes.

The fiow sheet in FIGURE 1 illustrates the process of preparing the thermoset material. Actually two individual processes are required because the thermoset waste materials are made available in two basic forms by manufacturers; one for finely divided dust-like material and another for chunk or laminated material. Since in some cases, the dust is highly undesirable on the part of the manufacturer'due to its explosive or highly volatile char acter, it must be saturated with water in transportation. In processing it for additive useage the dust must be dried and immediately conveyed to a storage hopper. Favorable drying results from the standpoint of safety as well as efiiciency are obtained by heat which is indirectly applied to the water suspended dust by a specially constructed dryer comprised of a suitable metal tube having a heating element wrapped around it and the heating element covered with a layer of insulating ma-v terial.

Chunks, laminates, or sheet stock must go through a longer process. in the first phase, as shown in the drawing, the larger pieces are crushed or broken in a rough mill or by a knife hog, for example. The crushing and breaking apparatus includes extra hard, extra wide hammers whose weight has been increased to three times the weight of standard hammers since the resinoids are extremely difficult to break up. In addition the hammer shaft diameters have been increased for heavy duty and correspondingly larger bearings have been installed. Standard hammer balance and location (including the number of hammers) have been completely altered to adjust for the regulation of the amount of fines or dust component produced. Also, the screens in the bottom of an ordinary hammer mill must be removed when grinding coarse grade materials since the material being milled in this process will block them up.

' Next, the material is sorted to remove impurities. brought out above, such materials as copper and the like must be removed since they will adversely affect certain oil well operations such as well treating and logging. Particles of copper are readily discernible in the material and may therefore be visually detected and manually removed. Ferrous metal pieces are often found intermingled with the raw material; these are removed by an electro-magnet in front of one of the mills. Also, excessive amounts of nylon, canvas (CRM), paper, etc., filler materials which are employed in industry with the thermoset materials as well as all postforming materials (thermoset materials still in B-stage) are removed in this stage of the process. -It should be noted, however, that all of this filler material or laminate base is not necessarily removed since such material enhances the barrier forming property of the additive of the present invention. In the size ranges given above, i.e., fine, coarse fine, etc., 0-35 of the material may be conventional industrial organic laminate base or filler material when such is included in the composition. However, an optimum percentage has been found to be about 19%.

After sorting, the material is sent to hammer mill #1, which rough hammers the material into smaller particles and passes it to hammer mill #2 where the particles are broken up into various sizes within the ranges desired. Removable, selective size screens are provided in this hammer mill which retard passage of any particles which are larger than the desired size. It is often necessary, for example, to screen the excess flock-like material off and to remove that portion which does not fit within the proper grading. From the second hammer mill the ground thermoset material is placed in a storage hopper.

When it is desired to remove my additive materials from the plant, they are transported through tubular conduits from the storage hoppers to a final set of screens and air separators which will finally determine the size of the particles that will go into the bagging apparatus.

FIGURE 2 schematically illustrates a double disk attrition mill which may be used in processing the chunky or laminated material which is initially placed in conduit and conveyed into a breaking apparatus comprising two opposed huller plates having very hard burrs on opposed faces. The huller plates are rotated by motors (50 horsepower, for example) operating in opposite directions. The huller plates are adjustable in that they can be moved closer together or separated depending upon the desired particle size. The size of the burrs 110, the amount of material being fed to the mill, and the speed of the plates also contribute to the final size of the particles being ground. This attrition mill may be employed in lieu of hammer mill #2 as described in connection with FIGURE 1, or in addition thereto.

The particles thus produced by my process are generally chip-like, flock-like, and sliver shaped.

APPLICATION OF LOST CIRCULATION ADDITIVE As illustrative of how my materials are utilized under actual drilling conditions and the results attainable therefrom, the following illustrative examples of actual chronological well histories are given: (phenol-formaldehyde used throughout the following examples).

Example 1A Galveston County, Texas:

Conditions-Well A Lime, Quebracho mud 4,300 ft. set 13%" casing Stuck pipe, cement No lost circulation At 8,500 ft. mud weight raised to 15.7 lbs. per gal. Drilled to 12,270 ft. with no trouble, set 9%" casing. Cemented by adding 20 sacks of thermoset (phenolformaldehyde) material of coarse fine grade.

Mud weight raised to 16.5 lbs. per gal.

l3 Tower treatment 10 sacks a day thermoset additive of same grade used sparingly when needed. Raised mud weight to 17.2 lbs. per gal. and drilled out from under pipe. At 13,300 feet, mud weight 17.4 At 14,000 feet, 10 bags each Tuf Plug, mica, and

thermoset additive of medium grade.

'At 14,340 feet, 10 bags each Tuf Plug mica and.

It was reported that this company never had a trouble.

free -well such as this one in this particular area.

Example 13 V In another wellin the same area in which the well of Example 1A was drilled, thermoset materials were used exclusively.

Conditions:

6,900 feet, set 13% casing.

8,100 feet, 14.0 lbs. per gal. mud weight.

9,100 feet, 15.0 lbs. per gal. mud weight.

9,700feet, 15.5 lbs. per gal. mud weight.

10,000 feet, 16.0 lbs. per gal. mud weight.

10,900 feet, 16.5 lbs. per gal. mud weight.

11,700 feet, 16.7 lbs. per gal. mud weight.

11,800 feet, 16.7 lbs. per gal. mud weight.

Added 15 sacks of thermoset materials of medium grade before running casing.

trouble free.

Drilled out under the casing, 17.2 lbs. per gal. mud

weight.

13,300 mud weight 17.4 lbs. per gal.

Lost circulation at 13,800 feet with mud weight 17.4

lbs. per gal. Mixed 78 sacks of thermoset additive of coarse grade and regained circulation at 13,860

' feet. Had gas kick and went up to 17.9 lbs. per

gal. mud weight.

Mixed 43 sacks of coarse fine thermoset additive; no loss of mud. Drilled ahead, 13,860 feet with 17.9 lbs. per gal. mud weight. Started 10 sack towerly treatment of coarse fine thermoset additive.

At 14,315 feet went over shaker then started 20 sack per day fine thermoset additive.

TD at 15,500 feet. Added 10 sacks thermoset additive of medium grade; no trouble, wire line ineluded. No trouble running pipe.

Total additive material used:

1 313 bags of thermoset additives Total mud cost-$67,982.00

of fine grade 3 pounds per barrel Set 9 /8 casing Lost return zone known to exist in this area between 6,800 and 7,300.

No trouble encountered with 4,200 feet open hole. Ran 16 pound cement.

5 I Example 3 Hidalgo County, Tobasco Field, Texas:

Conditions- Broke over to low lime mud, 10.4 mud weight. 38 viscosity, 12%" hole at 4,255 ft.

1,813 ft. of 13% surface casing.

Added thermoset additive of coarse fine grade at 6,200 ft., 110 sacks-6 lbs. per barrel. Tower treament, 2 sacks. 15 Drilled 12%" hole to 7,500 ft. to 14.2 mud weight, 49 viscosity. Set 9%" casing.

No trouble.

Example 4 Newton County, Texas:

Conditions At 1,537 ft., set 13%" casing.

Drilled to 10,152 ft.

Had trouble with lost return all the way down. Lost considerable rig time. Treating initially with mica and Tuf Plug.

At 10,152 ft., 11.2 mud, 50 viscosity, 5.4 water loss, 12%" hole set liner. Drilled out and started treament, fine Tuf Plug and fine mica, two sacks per tower. Mud weight 15.4.

At 10,309 ft., started treatment of thermoset additive (fine grade), 8 sacks per tower. Lost returns at 10,505 ft. Mixed 69 sacks slurry, medium thermoset additive and regained circulation.

Example 5 Starr County, Texas:

Thermoset additive used here to prevent lost circulation rather than terminate it. i

Fine grade thermoset additive used from /2 to 1 lb.

per bbl. of mud drilling 8%." hole.

Mud weight from 6,000 to 8,300 ft. ranged from 11.4 to 13.6 lbs. per gal. at 8,300 ft.

10 drill stem tests and two electric wire line logs ran.

7 casing set and cemented with 15 /2 lbs. cement from 8,300 to 4,200 ft.

Drilled out 7" casing, mud weighing 14 /2 lbs. per gal. and carrying concentration of 1 lb. per bbl.

fine grade thermoset additive Drilled to 9,000 ft., set and cemented liner without any lost circulation problems whatsoever in an area known to have potential lost circulation formations.

Example 6 Results of Stormer viscosimeter tests conducted to determine the effects of my lost circulation additives on drilling muds' were asfollo-ws:

[initial mud 8.85 lbs. per gal. Viscosity 30 cp.]

Viscosity, Cps.

Fine 32 34 39 44 Coarse Fine 35 44 49 i 54 Medium; 82 34 41 51 Coarse--. 46 54 59 61 Super Coarse 44 54 56 59 4 Concentration, lb. per bbl. 3 6 9 12 The water absorption characteristics of thermoset materials in general, and particularly phenol-formaldehyde used in the above viscosity tests, have been proven to be extremely low (three to five tenths of one percent). Therefore, the slight increase in viscosity at the concentratrons employed can be attributed to (1) surface adhesion or surface wetting due to the greatly increased contact areas, (2) increase of solids in the drilling mud by the direct addition of an inert solid material, and (3) the Stormer viscosimeter is subject to plugging by the larger solid particles and this creates an impedance to fiow of the liquid being tested and results in an apparent increase in viscosity that is not realistic. These conditions are inherent in the viscosity testing of any drilling mud additives. In comparison with other materials, the above test results show a remarkably slight effect on drilling mud viscosities which can be attributed primarily to the low water absorption characteristic of the additive material.

Example 7 lb per bbl. caustic l 1 2 2 2 2 lb. per bbl. additive- 3 3 5 5 6 6 coarse med. coarse med. coarse none 0) temperature of.

I Test time (hrs) 2 Eflcet none lb per bbl. loss in weight. per bbl. loss in weight.

a 0.1 b 0.4 n .35 per bbl. loss in Weight.

Example 8 Another viscosity determination was made for phenolformaldehyde dust particles sieved through a 375 mesh screen, using the same mud as specified in Example 7.

Mud sample-viscosity:

1 lb. per bbl. additive 1.3 cp 3 lb. per bbl. additive l4- op 6 lb. per bbl. additive 15 cp Filtration losses may also be substantially completely prevented by my thermoset resinoid additives employed either alone or in combination with an organic material such as CMC. I prefer to employ, for this purpose powdered or very finely ground particles of C-stage phenolformaldehyde (although other thermoset materials as above stated give good results) mixed with particles of organic material such as powdered ethylcellulose and methylcellulose. A preferred composition of this embodiment of the present invention is 50-98 percent by weight of the phenolic powder and the remainder being sodium carboxymethylcellulose. More specifically the preferred amount of phenolic powder is 95 percent by weight. Sodium ortno silicate, ethylcellulose, propylcellulose or mixtures thereof may also be used as the organic material with powdered particles of any thermoset material particularly those mentioned above. The small size C-stage particles can be obtained by ball milling or other suitable process. There is no practical limit on how small these particles may be while an upper size limit of particles passing a 100 Tyler mesh screen retained on a 150 mesh screen, should be maintained for best results. Particles of larger sizes may be utilized as will hereinafter appear when lost circulation is also present to a certain extent, but in general the 150 mesh size is sutficiently large to control any filtration losses occurring through an ordinary mud sheath and if large particles are not necessary it is usuallythe better rule to avoid using them. A preferred particle 1 3 gradation for this filtration loss additive is as follows:

Parts by weight 6 to mesh 1 150 to 200 mesh 16 200 to 250 mesh 17 250 to 300 mesh 17 300 to 325 mesh 17 325 to 350 mesh 17 This gradation is obviously not critical when it is considered that varying geological conditions and well drilling operations will tend to vary the effect thereof. Such a gradation however, would provide particles for bridging all sizes of openings in a formation not having openings large enough to take mud, and would therefore be suitable under more common drilling conditions.

The powdered phenolic material employed in this additive is preferably substantially pure i.e., it contains no laminate base material or filler material such as may present in the lost circulation additive although such material may be present in several parts by weight without materially altering the results obtainable.

As another example of the filtration loss additive, a size range is maintained in which about 50% by weight of the thermoset material is 325 Tyler mesh or smaller, while the remainder is evenly distributed throughout the range of 100325 mesh.

The mixture of thermoset particles and organic material may also be used in combination with the graded resinoid lost circulation additives of this invention.

The resinoid particles exhibit a tendency to absorb organic colloids such as CMC upon their surfaces. However, the exact reaction or attraction between the two elements, i.e., the resinoid material and organic COllOld material, is not known at this time. In an aqueous solution, the colloid will hydrate to form a film over the surface of the resinoid particles in solution. This film attracts and holds hydrated molecules of colloid and the coated particles that are present. For example, with preferred CMC and phenol-formaldehyde the reaction or attraction may possibly be explained by the theory that attractive forces between the particles are electrical and vary continuously with the structure thereof to provide a rearrangement or change in the sodium carboxymethylcellulose which causes an improved filter cake on the well bore as these particles become a part thereof. Whatever the theory, it has been discovered that colloidal cellulosic material and powdered plastic combine together to form particles having the strength of the resinoid and the preventative filtration loss property of both the resinoid and the cellulosic material. Not only do the small size particles improve typical bentonite or other known mud filter cakes deposited on the borehole wall by effectively sealing the smallest pervious openings in the filter cake, but they also bond the clayey filter cake particles more strongly together. In other words, instead of using big particles to bridge big openings as in the lost circulation situation, this powdered mixture bridges small gaps or weak places in a mud sheath so as to provide a more impermeable sheath having a very desirable gelatinous surface formed thereon resulting from the films of hydrated colloidal material formed over the powdered C- stage resinoid particles. While the attraction of the particles can be detected in the mud, it is much more pronounced after the particles. have been deposited in the mud sheath under pressure. Of particular importance is the fact that any coagulation of the particles while suspended in the well fluid does not alter the viscosity or other properties of the well fluid in any appreciable manner.

In a recent test, a mixture of 5 lbs. sodium carboxymethylcellulose and 95 lbs. of C-stage phenol-formaldehyde was added to a drilling fluid at a rate of 5 lbs. per bbl. and the resultant filtration loss was zero as compared to other prior art additives, the best of which permitted .a loss of at least 3 cc. or

17 7 more using the same amount of material lbs.) .per barrel. The prior art additives also contained much more sodium carboxymethylcellulose than the additive of the present invention. This material was thought by many to be the only element controlling filtration losses; but with the additive of the present invention tests have yielded the conclusion that the powdered resinoid such as phenol-formaldehyde combines tion loss which will obtain results much better than when cellulosic material such as sodium carboxymethylcellnlose is used by itself or with other known materials. The amount of the resinoid-organic material mixture or powdered resinoid alone to be used in a well will depend on the amount of filtration loss and the condition of mud sheath, the formation characteristics, and operating conditions such as temperature and pressure. In general, 5 to 25 p.p.b. of drilling fluidwill prevent normal losses. However, more or less additive may be used, and this of course, can only be determined with reference to a particular job and to the degree it is desired to eliminate filtration losses.

Frequently drilling conditions require control of both filtration losses and lost circulation. In such situations particularly good results are obtained by adding to the drilling fluid, a mixture of the powdered filtration loss additive comprising powdered C-stage resinoid and organic material, previously described, and a lost circulation additive comprising C-stage resinoid particles. The

combined additive thus formed has the properties and obtains the advantages of both the gradated C-stage additive and the colloidal resinoid organic material additive. The additives cooperate to form a substantially impercirculation additive which may be determined as being most suitable under the particular conditions, and 2.60% resinoid-organic material mixture. Here again I prefer in the latter fraction, phenol-formaldehyde and CMC in amounts described above.

Recent tests, typical results of which are tabulated below, performed according to the API Code at Oklahoma State University, Stillwater, Oklahoma, indicated a mixture of 5 lbs. per barrel of this combination additive in its preferred form would seal holes up to 0.120 inch under a maximum pressure of a 1000 p.s.i. Note from the tables that there has been no appreciable change in mud properties such as mud weight, pH, gel strength, viscosity, etc. The water loss reduction from 25 cc. to less than 1 cc. illustrates the effectiveness of this additive in preventing filtration losses. A study of the curve shown in FIGURE 4 indicates that larger slot sizes may be plugged with larger particles and greater amounts of this sealing agent. The larger particles employed in these particular tests ranged in size from 4 to with the organic material to provide an evenbetter filtra- I I The sealing capability -of the outstanding features of this additive.

18 of only a small quantity is one In addition, the combination of particle sizing plus colloidal additions has the ability to seal both large and small openings to the extent that neither mud loss nor appreciable filtration loss occurs. Tests indicated that this additive was effective in both fresh and salt water mud, also.

FIGURES 3 and 4 illustrate the sealing ability of this additive relative to other lost circulation materials known to the prior' art. A study of this chart indicates that small amounts of the additive, for example 5 lbs. per barrel,

-can seal the same size fracture, 0.120 inch, as can larger concentrations from 8 to lbs. per barrel of other available loss circulation material. Fractures up to 0.22 inch were sealed by the addition of 10 lbs. per barrel. A material is judged to be successful at a given size if it will plug the slot to hold 1000 p.s.i. differential without leaking. The range of phenolic particles between 4 I and mesh is substantially closer to the size range of the listed prior art additives and therefore provides a more accurate comparison of the improved results obtained bythe present invention over the prior art. However, it should be noted that, as brought out above in I bination filtration loss, lost circulation additive.

Tables I and II--Eifect of additive on drilling fluid. (The test additive was a mixture of phenol-formaldehyde particles ranging from 4 to 140 mesh and sodium carboxymethylcellulose representing 2.6% of the total.)

TABLE I Fresh Water Bentonite Mud Fresh Water Plus Five Bentonite Pounds Per Mud Barrell of Chosen Mixture Water Loss-.. 25 cc Less than 1 cc. V1scosity 11.5 cps"... 28 cps. Initial Gel Strength 19 gms 15 gms. Final Gel Strength, 35 gms 35 grns. pH 7.2 7. Filter Cake Me. Mud Weight 8.74. 8.78.

TABLE II Fresh Water Fresh Water Bentonit'e Mud Bentonite Mud Contaminated Contaminated with 50,000 ppm. with 50,000 p.p.m. Salt Salt Plus Five Pounds Per Barrel of Chosen Mixture Water Tms Less than 1 cc. Viscosity 53 cps. Initial Gel Strength 45 gms. Final Gel Strength 5 gmS. nH 7 7. Filter Cake; la. Mud Weight 8.85.

My materials may be utilized advantageously in cement slurn'es in the form of relatively large particles in the order of /zinch diameter or in dust form. They can be added during preparation ofthe slurry or can be mixed with the slurry in the mud pit for example just before it enters the well. In casing cementing practices, the slurry is circulated down the well through a pipe and then up the well around the, outside of the pipe. It may, in some operations, be circulated to the surface on the outside of the pipe. I prefer to maintain a suitable concentration of bridging material in the slurry at all times sufficient to bridge and seal openings as they are formed or otherwise encountered. The particles for this applica- Example A series of tests were run on neat cement slurries to determine the effects on density, setting time and compressive strength using different weightsand sizes of my materials.

The following tests were conducted using a Halliburton Consistometer to determine the setting time and a Baroid mud balance to verify the density calculation. The compressive strength was determined by breaking test cylinders which were cured in a water bath at a temperature ranging from 82 to 86 F. at atmospheric pressure according to ASTM standards. The setting times were all determined at a temperature of 140 F. and atmospheric pressure.

The mixing procedures were as follows for the tests:

First a water-to-cement ratio was calculated to produce two 15.5 lbs. per gal. cement slurries with a final volume of 2.5 gals. each. Ground thermoset material (phenolformaldehyde in this case) in dust form was added in amounts of 7.63 and 15.35 pounds per barrel. Next, the cylindrical cups from the Halliburton Consistometer were filled with the revolving paddle in place and then capped. They were then fitted into the case containing a worm gear driven by an electric motor. An electrically heated water bath surrounds the cups and was kept constant at 140 F. As the paddles revolved at constant speed, the thickening cement slurries exerted a thrust that is transmitted through a movable drag head on the top of each cup to a lever arm 1, causing the latter to be deflected from its normal vertical position. The amount of deflection of the lever indication at any time is thus a measure of the viscosity of the cement slurn'es, and a scale on which observations of the amount of deflection are made is calabrated to read directly in centipoises of absolute viscosity. The test is continued until a reading of 10 (approximately 10,000 centipoises) is attained, which is regarded as the limit of pumpability. While the setting times were being determined for two slurries, two test cylinders were filled (diameter 6 inches, length 12 inches) and rodded according to ASTM standards. The test cylinders were then allowed to set for 24 hours, but were kept damp during this time. After 24 hours, the cylinders were peeled and placed in a water bath for six days before breaking. After conducting later tests it was determined that an initial density of 14.0 pounds per gallon slurry should be used. All other tests were thereafter conducted using this density. In addition to dust, five other thermoset grinds were tested ranging from separate slurries.

The results of these tests show that resinoid dust can be advantageously utilized as an additive for cement slurries to reduce their density. Thirty pounds per barrel of dust to an initial cement slurry of 14.0 lbs. per gal. will yield a compressive strength in the order of 1,050 psi. If depth is a factor then the amount of additive may be reduced which will give an increase in setting time, compressive strength and density, but will decrease the yield. Forty pounds per barrel may also be used to reduce the final mixture to 11.0 pounds per gallon, however, the setting time is reduced to the point where it is practical to use retarders such as sodium tannate, gypsum, sugar, and lime. Of course, the time of thickening, setting and hardening may also be prolonged in the process of manufacturing by coarser grinding of the cement clinker, or by altering the chemical composition. The use of ice water in mixing cements will also tend to reduce slurry temperature in deep wells and thus prolong the setting time. For a cement slurry of 14.0 lbs. per gal. density, 30 lbs. per bbl. of thermoset dust material will decrease the density 2.0 lbs. per gal. or 14.3 percent while the compressive strength is decreased to 1,050 p.s.i. Thus, a good cement slurry mixture is produced when a decrease in density is desired without too much decrease in compressive strength for setting times.

The effect of the larger particles, however, on cement slurries is a much lesser reduction in density or setting time, but also a much lesser reduction in compressive strength. Therefore, I prefer to employ particles of larger sizes when a decrease in density is not needed, but yet control or prevention of lost circulation is desired. During these tests it was seen that my additives are evenly dispersed throughout a cement slurry and that the properties of the cement slurries were not sufiiciently altered, although there was a slight decrease in compressive strength.

In cement slurries the same general concentrations of materials for eliminating or preventing lost circulation maintained in drilling fluids as described above, are likewise applicable. A concentration sufficient to provide a large safety factor over the minimum concentration estimated to be effective, and yet which will not alter the desirable properties of the slurry, is generally considered advisable.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. An additive for a well servicing composition of the 'class consisting of oil base drilling muds, water base drilling muds and cement slurries, said additive consisting essentially of size gradated particles of ground C-stage commercial resinoid material, a major proportion of said particles being relatively flat, chip-shape in appearance and sufiiciently thick as to exhibit substantial flexural strength when bridging an opening in the borehole wall of the well, the size of said particles being sufliciently large to be retained on a 150 US. sieve and selected so that the largest size thereof will be pumpable along with said composition and capable of bridging the largest expected formation opening for the particular job in which the additive is used. 7

2. The additive as defined in claim 1 wherein the particles range in size from approximately 150 US. sieve to a longest dimension of not over about 2 inches.

3. A well servicing composition comprising the combination of a first material selected from the class consisting of an oil base drilling mud, a water base drilling mud and a cement; and an additive mixed with said first material in an amount sufficient to substantially reduce circulation losses of said first material; said additive containing an amount of ground particles of a C-stage resinoid material effective to reduce lost circulation, a major portion of said particles being relatively fiat, chip-shape in appearance and sufficiently thick as to exhibit substantial flexural strength when bridging an opening in the borehole wall, the size of said particles being sufficiently large to be retained on a 150 US. sieve and selected so that the largest size thereof is pumpable and capable of 21 rial ranges from between approximately 150 US. sieve to a longest dimension of not over about 2 inches.

5. The well servicing composition as defined in claim 3 wherein the C-stage resinoid material particles are present in a quantity of at least one quarter pound per barrel of said first material.

6. Awell servicing composition as defined in claim 3 together with a filtration prevention additive composed of powder sized particles of a Csstage resinoid material no larger than about 350 'B ler mesh mixed with a material selected firom the group consisting of hydroxyethylcellulose, sodium carboxymethylcellulose, propylcellulose, and sodium ortho-silicate, the filtration additive being composed of 5098% by Weight of the resinoid material and 250% of the material selected from said group.

7. A well servicing composition as defined in claim 3 together with a seepage prevention additive composed of thin particles of a tough, pliable filler material covered with a C-stage resinoid material and having a maximum length on the order of three quarters of an inch, said filler material being present in amount of at least one 7 quarter pound per barrel of said first material.

8. The well servicing composition as defined in claim 3 wherein the filler material is kraft paper.

9. A method of servicing a well comprising circulating in said well a composition comprising a slurry, and an additive ranging in amounts from lbs. per bbl. to as many pounds per bbl. as is necessary under the geological conditions present to reduce lost circulation, said slurry being of the class consisting of aqueous drilling fluids, non-aqueous drilling 'fluids, and cement slurries, and said additive consisting essentially of particles of a C- stage resinoid material having a fiexural strength of between 6,000 and 80,000 lbs. per sq. inch, capable of resisting temperatures of at least 280 F., and being relatively insoluble and infusible, and at least 3% by weight of said particles being relatively flat, chip-shaped in appear'ance and suificiently large to be retained on a 150 US. sieve.

10. In a process for drilling a well with well drilling tools wherein there is circulated in the well a composition comprising a slurry in a fluid form to render the slurry circulat-able, the method of forming a filter cake on the wall of said well to decrease the loss of said slurry into surrounding earthen formations which comprises admixing With said slurry an additive consisting essentially of ground particles of C-stage resinoid material, a major portion of which are relatively flat, chip shape in appearance and sufliciently thick as to exhibit substantial flexural strength when bridging openings in said earthen formations, the size of said particles being sufiiciently large to be retained on a US. sieve and selected so that the largest size thereof will be pumpable with said slurry and capable of bridging the largest expected formation openmg. a

11. The process as defined in claim 10 wherein the additive consists essentially of ground particles of laminated C-stage commercial resinoid wastage material including chemically inert filler materials incorporated in the laminated material by the lamination manufacturer.

12. The process as defined in claim 10 wherein the C- stage resinoid material particles range in size from between approximately 150 US. sieve to a longest dimension of not over about 2 inches.

13. The process as defined in claim 12 wherein the C- stage resinoid material particles are present in a quantity of at least one quarter pound per barrel of said slurry.

Fluids-Revised Ed. 1953. Texas, pages 562 and 563.

Gulf Publ. Co. of Houston, 

3. A WELL SERVICING COMPOSITION COMPRISING THE COMBINATION OF A FIRST MATERIAL SELECTED FROM THE CLASS CONSISTING OF AN OIL BASE DRILLING MUD A WATER BASE DRILLING MUD AND A CEMENT; AND AN ADDITIVE MIXED WITH SAID FIRST MATERIAL IN AN AMOUNT SUFFICIENT TO SUBSTANTIALLY REDUCE CIRCULATION LOSSES OF SAID FIRST MATERIAL; SAID ADDITIVE CONTAINING AN AMOUNT OF GROUND PARTICLES OF A C-STAGE RESINOID MATERIAL EFFECTIVE TO REDUCE LOST CIRCULATION, A MAJOR PORTION OF SAID PARTICLES BEING RELATIVELY FLAT, CHIP-SHAPE IN APPARANCE AND SUFFICIENTLY THICK AS TO EXHIBIT SUBSTANTIAL FLEXURAL STRENGHT WHEN BRIDGING AN OPENING IN THE BOREHOLE WALL, THE SIZE OF SAID PARTICLES BEING SUFFICIENTLY LARGE TO BE RETAINED ON A 150 U.S. SIEVE AND SELECTED SO THAT THE LARGEST SUZE THEREOF IS PUMPABLE AND CAPABLE OF BRIDGING THE LARGEST EXPECTED FORMATION OPENING FOR CAUSING LOSS OF SAID FIRST MATERIAL. 